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Manufactoring > Plastics > Flashcards

Plastics Flashcards

1
Q

what are some of the applications of plastic

A

construction
packaging
plastic lumber
automotive

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2
Q

what are the advantages of plastic processing

A

no further shaping is needed
less energy is required
painting is normally not required
handeling of product is simplified

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3
Q

disadvantages of plastics

A

low strength
low modulus of elasticity
limited useful thermal range
can degrade ehen subjected to radiation
fragile
dimensional instability
flammable
suceptible to chemical attack
may have associated health risk

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4
Q

advantages ofd the plastic material

A

high corrosion resistance
good insulating properties
good strength to weight ratio
ease of processing and reprocessing
capable of being rigid or flexible
can be transperant, translucent, or opaque

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5
Q

what are the 3 types of polymers

A

thermoplastics
thermosetting
elastomers

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6
Q

what are thermoplastics

A

they can be heated, cooled and reheated.
can be recycled
dont crosslink when heated

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7
Q

what are the 3 ways crosslinking is accomplished

A

tempurature
catalyst
mixing

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7
Q

what are thermosets

A

undergo curing when heated
crosslinking happens when heated
cannot be remelted

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8
Q

what are elastomers

A

caple of large elatic deformation

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8
Q

why are thermosets sometimes better then thermoplastics

A

more rigid
brittle
more resistant to common solvents
capable of higher surface tempuratures

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9
Q

what makes elastomers have the incrediable elatic properties

A

long molecules
dergree of cross linking is lower then thermosets

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10
Q

what are the 2 molecular structures for polymers

A

crystalline
amorphous

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11
Q

what is the properies of crystline steructure

A

not clear
opaque or translucent plastic
chains packed closely together

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12
Q

what is the properies of amprphous steructure

A

spagetthi type structure
clear plastics

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13
Q

what are the shaping processes for platics

A

injection molding
extrustion
compresstion molding
blow molding
rotational molding
calendering
composites

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14
Q

what is injection molding

A

a process wheere a heated polymer is forced into a cavity

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15
Q

injection molding facts

A

very similar to die casting
complex shapes possible
high tool cost
long lead time
economical for high volume production
typically for thermoplastics

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16
Q

what are the 3 units in the injection molding machine

A

injection unit
mold
clamping unit

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17
Q

how does the injectioln molding process work

A

1) mold is closed
2) melted plastic injected in cavity
3) screwback
4) mold opens and part is released

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18
Q

what are the 2 parts of the mold

A

cavity: internal design
core - external design

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19
Q

why are the 2 halves of the mold called the hot and cold sides

A

hot side- material is injected though this side
cold side- materials is cold and enjection system is only on this side

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20
Q

what is shrinkage

A

as the polymes cool they will shrink and the amount of shrinnkage is dependant on the type of plastic

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21
Q

what are the shrinkage factors

A

injection pressure
compaction time
molding tempurature
fillers tend to reduce shrinkare

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22
Q

what are the 4 common injection molding defects

A

short shott
flash
sink marks/voids
weld lines/knit lines

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23
Q

what are the causes of short shot

A

not enough plastic
to cold
to slow to inject

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24
Q

what are the causes of flash

A

spaces is mold
fhigh injection pressure
melt tempurature to high
mold wearing

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25
Q

what are the causes of sink marks

A

thick mold sections

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26
Q

what are the causes of weld lines

A

temp to low
speed to love

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27
Q

what is a die

A

a tolol used to cut/form material into desired form/shape

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28
Q

what is extrusion of plastic

A

compression process in which flow of material is forced through a die

29
Q

what are some applications of extrusion

A

pipes
hose
structural shapes
sheet/film
continuos filiment
coated elctrical wire

30
Q

what are the main components of the extruder

A

barrel
screw
die

31
Q

what are some common die profiles

A

solid
hollow
wire/cable coating
sheet/film
filaments

32
Q

what is viscoelasticty

A

the shape memory of the material

33
Q

what is an example of a solid profile

A

rounds
squares
ireggular cross section

34
Q

what happens when solid profiles are extruded

A

material is still soft after die
to mnimize visoelasticy the die is made long

35
Q

what is an example of a hollow profile

A

pipes
hoses
any cross section with a hole

36
Q

what happens when hollow profiles are extruded

A

mandrel required to form internal shape

37
Q

what happens when wire/ cable coating is extruded

A

pulled at high speed
vaccum is drawn to promote adhesion

38
Q

what is sheet/film made of

A

film- thermolplastics
sheet- thermorming

39
Q

what are some applicatoiooons of film

A

packaging
pool covers
liners for irregation

40
Q

what are the processes for sheet/film

A

split die extrusion
blown film extrustion
calendaring

41
Q

what is split die extrusion

A

conventional extrusion but uses narrow slit as die opening
uniformity is sometimes a problem

42
Q

what is blown film extrusion

A

combines extrusion to produce of thin film

43
Q

what is the process of blown film extrusion

A

extrusion of tube
tube is drawn to upward and expnded by air at the same time
air pressure kept constant to keep thickness of film

43
Q

what is the frost line

A

marks the position where solidification occurs.

44
Q

what is calendaring

A

a process for producing sheet/film out of rubber or rubbery thermoplastics

45
Q

what is the process of calendaring

A

feedstock is passed through the series of rolls to reduce thickness to desired games

46
Q

calendaring facts

A

expensive equipment
high productiomn rates
has good surface finish and accuracy

47
Q

what are applications of calendaring

A

pvc flooring
shower curtians
table cloths
pool liners
inflatable toys

48
Q

what sis the comppression molding process

A

1) material is loaded
2) material is compressed and cured
4) part is ejected amd removed

49
Q

what are the possible molding compounds availble

A

powders
pellets
liquid
preform

49
Q

compression molding facts

A

used with thermosets and elastomers
used for rubber tires an dpmc parts
marterial is preheated to shorten cycle times
mold is heated to help cure the material

50
Q

compression vs injection molding

A

compession: molds are simpliar
injection: shorter cycle times and higher production rates

51
Q

what are the common molding materials in compression molding

A

eppoxies
urethanes
elatomers
phenolics
melamine

52
Q

applications for compression molding

A

electric plugs
pot handles
electrical sockets
dinnerware plates

53
Q

what is tranfer molding

A

very closely related to compression molding

54
Q

what are the 2 different types of transfer molding

A

pot tranfer molding
plunger transfer molding

55
Q

what is the basic transfer molding process

A

1) material sis loded into chamber
2) pressure applied as polymer is pressed into cavity
3)part is ejected

56
Q

pot vs plunger

A

pot: injected through vertical sprue channel
plunger: injected through heated well

57
Q

what is blow molding

A

a process where air pressure is used to inflate the soft plastic
an important process for making really thin hollow parts

57
Q

what is the process of blow molding

A

1) create tube (parson)
2) add heated parison into tube
3) clos the mold
4) add the compressed air into the mold
5) trim product and remove from mold

58
Q

what are the 3 differnt blow molding procsses

A

injection
extrusion
stretch

59
Q

what are the advantages of extrusion blow molding

A

reduces stresses
has weight reduction properties
reduction on waste
reduced cooling times

60
Q

whats is speciall about blow molding

A

only can be used with thermoplatics

61
Q

what is rotaionial molding

A

a process that uses gravity inside a rotating mold to form a holllow shape
its a simple but slow process

62
Q

what polymers can be used in rotational molding

A

mainly for thermoplastics but can be used for elastomers and thermosets

63
Q

what is the process of rotational molding

A
  1. material is loaded into mold
  2. mold is closed, heated, and rotated on 2 axies
  3. plastic is colloed while still spinning
  4. part is removed
64
Q

what is thermoforming

A

flat thermoplastic film/sheet is heated or deformed into desired shape using mold

65
Q

what is the process of vacumn thermoforming

A
  1. plastic is heated
  2. sooftened platic is placed over negitive mold
    3.a vacumn effec draws the sheet into the cavitys
  3. plastic hardens and shape is removed
66
Q

postive vs negitive molds

A

positive- inerior matched the countour of the mold
negive- the exterior will math the contour of the mold

67
Q

what are the general design considerations for plastic

A

strength/stiffness
impact resistance
service tempuratures
thermal expansion
degradtion

68
Q

what are the design considerations for extrusion

A

walol thickness
hollow sections
sharp corners
shrinkage
die swell

69
Q

what are the design considerations in injection molding

A

economic quantities
part complexity
wall thickness
corner radii and fillets
ho;es
shrinkage
parting line location
slides/side actions
draft angles
tolerances

Manufactoring (9 decks)

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